1. Field of the Invention
This invention relates to industrial pumps of the centrifugal type, and specifically relates to a rotor assembly of a pump which is configured to counteract deleterious centrifugal forces exerted from within the rotor assembly and thereby improve seal life and increase allowable suction pressures.
2. Description of the Related Art
Centrifugal pumps are well known and widely used in a variety of industries to pump fluids or liquid/solid components of fluid mixtures. Centrifugal pumps, particularly those of the pitot tube type, generally comprise a pump housing having an inlet and an outlet and a rotor assembly which rotates within the pump housing by means of a drive unit. More specifically, the rotor assembly comprises a rotor, sometimes called a xe2x80x9cdrum,xe2x80x9d and a rotor cover which attaches to the rotor to form a rotor chamber within which a pitot tube, or pickup tube, is stationarily positioned. Fluid is directed through the pump inlet into the rotor chamber and as the rotor assembly rotates, the fluid is directed toward the inner periphery of the rotor chamber as a result of centrifugal forces. The fluid is intercepted by the stationary pitot tube and fluid moves through the inlet of the pitot tube and toward the outlet of the pump for discharge.
Typical centrifugal pumps of the pitot tube type are disclosed in U.S. Pat. No. 3,822,102 to Erickson, et al., U.S. Pat. No. 3,960,319 to Brown, et al., U.S. Pat. No. 4,161,448 to Erickson, et al., U.S. Pat. No. 4,280,790 to Crichlow, U.S. Pat. No. 4,332,521 to Erickson and U.S. Pat. No. 4,674,950 to Erickson. In the pumps disclosed in the referenced patents, a rotor assembly generally comprises a first rotor member, sometimes referred to as the xe2x80x9cdrum,xe2x80x9d which is attached to a drive unit, and a rotor cover which is secured to the first rotor member to provide an inner rotor chamber. A central opening is formed in the rotor cover through which the stationary pitot tube extends. Most conventional rotor covers are flat, or planar, as measured from the hub of the rotor cover to the peripheral edge of the cover. That is, the hub and the peripheral edge of the rotor cover lie in a common plane which is perpendicular to a plane directed along the longitudinal axis of the rotor assembly.
The conventional planar configuration of rotor assemblies, and particularly rotor covers, has been dictated in large part by manufacturing considerations since planar rotors and rotor covers are easier to cast and machine. However, conventional rotors and rotor covers are subject to axial deflection within the pump casing as a result of forces exerted by fluid on the rotor chamber. That is, suction pressures and centrifugal pressures exerted by the fluid against the walls of the rotor chamber, especially against the circumferential wall of the rotor chamber, cause the rotor to expand radially outwardly. A corresponding axial deflection occurs in the rotor cover and the end of the rotor opposite the rotor cover. The axial deflection or movement of the rotor end and rotor cover increases as the rotational speed of the rotor assembly increases. The resulting axial deflection or movement of the rotor assembly exerts pressure on the seals associated with the rotor cover and not only limits rotational speeds in the rotor assembly, but also degrades the seals, thereby shortening the serviceable life of the seals. Further, the resulting deflection of the rotor assembly limits the suction pressures within the rotor chamber.
The alteration of the rotor assembly experienced in conventional pitot tube pumps as a result of inefficient design limits the operating speed of the pump. High rotational speeds and high suction pressures are typically not achievable in conventional rotor assembly designs without accelerated degradation of the seals associated with the rotor assembly.
Thus, it would be advantageous to provide a rotor assembly for a pump which is configured to resist axial deflection in the rotor cover and rotor end to thereby enable the pump to be operated at higher speeds with little or no reduction in suction pressure and with no degradation of the seals associated with the rotor assembly.
In accordance with the present invention, a rotor assembly for a centrifugal pump is configured to counterbalance the centrifugal forces exerted on the rotor assembly to limit axial deflection of the rotor and rotor cover. The rotor assembly disclosed herein is adaptable to any number of centrifugal pump designs for use in a variety of applications, but is described herein with respect to pitot tube pump designs as merely one exemplary application.
The rotor assembly of the present invention generally comprises a rotor member structured to be secured to a drive unit, such as the drive shaft of a motor, to impart rotation to the rotor assembly. The rotor member, the interior of which is generally bowl-shaped, has an end wall to which the drive unit is attached and an upstanding circumferential wall extending from the end wall. The rotor assembly also includes a rotor cover which is circumferentially sized to approximate the circumference of the rotor member and is attached to the rotor member along the circumferential wall thereof. The rotor member and attached rotor cover provide a rotor chamber into which fluid for processing is introduced during operation of the pump. The rotor assembly is sized to be received within the housing of a centrifugal pump and is rotatable therein.
The rotor assembly of the present invention is particularly configured to counterbalance the centrifugal pressures and suction pressures exerted by fluid within the rotor chamber which causes the rotor assembly to expand radially and the end wall and/or rotor cover to deflect axially, as described previously with respect to conventional rotor assemblies. Specifically, at least one end (i.e., the end wall or rotor cover) of the rotor assembly is configured to be non-planar in structure such that as centrifugal pressures exerted on the circumferential wall of the rotor member radially expand the rotor assembly, deflection of the configured end wall and/or rotor cover is limited or prevented.
As used herein, xe2x80x9cnon-planarxe2x80x9d means that the rotor cover is angled from near the central axis of the rotor cover toward the circumferential surface of the rotor assembly in the direction of the rotor member end wall or, similarly, the rotor member end wall is angled from near the central axis of the rotor member toward the circumferential surface of the rotor assembly in the direction of the rotor cover. Thus, xe2x80x9cnon-planarxe2x80x9d is meant to include an end wall or rotor cover which is conical in shape or and end wall or rotor cover the outward facing surface of which is arcuate or curved. Either the end wall or the rotor cover may be non-planar, or both may be non-planar in configuration. It may be preferred that the especially configured end wall or rotor cover be uniformly shaped (i.e., non-planar) along the outward facing surface and inward facing surface thereof such that the thickness of the end wall or rotor cover, from a point near the central axis thereof to near the circumferential wall or peripheral surface of the rotor assembly, is substantially uniform in thickness. By xe2x80x9csubstantially uniformxe2x80x9d is meant that the hub portion of the end wall or rotor cover (i.e., that area surrounding the central axis of the end wall or rotor cover) and/or the peripheral region of the end wall or rotor cover, and the region extending therebetween, may be comparatively more or less thick to provide stability to the rotor assembly.
The advantages realized in the configuration of the rotor assembly of the present invention are better understood in reference to the drawings and detailed description set forth hereinafter.